The present invention relates to diplexers for full duplex communication and, more specifically, to a reconfigurable, tunable, band-selectable diplexer which may be integrated directly with the antenna elements and feed networks of an array antenna that may be used for simultaneous transmission and reception.
High data rate, communications systems, both military and commercial, generally operate in a full duplex communications mode. A diplexer is typically used in a satellite dish antenna to separate the transmit and receive frequencies so that the transmit channel does not overpower or saturate the receive channel. These diplexers are expensive, bulky filters. Moreover, it is not practical to place one behind every antenna element in a large phased array antenna.
An interference problem arises when both transmission and reception are required simultaneously. One solution to this problem has been to utilize separate antenna arrays for reception and transmission. This solution provides adequate isolation between received (Rx) signals and transmitted (Tx) signals but requires extra space to implement two arrays. In addition, this approach is also expensive. The cost of a full duplex antenna array could be reduced if some filtering and/or channel isolation could be implemented in the antenna elements themselves. These additions to the antenna structure, combined with the addition of simple filters at the transmitter and receiver themselves, could provide lower-cost, full duplex antenna arrays with the necessary channel separation and isolation.
It is therefore an object of the invention to provide a reconfigurable, tunable diplexer for use in communications antenna systems.
It is a further object of the invention to provide a reconfigurable, tunable diplexer for use in antenna systems, which may selectively operate in more than one communications band.
It is another object of the invention to provide a reconfigurable diplexer for use in antenna systems which includes a tunable, multi-pole comb filter.
It is another object of the invention to provide a reconfigurable diplexer for use in antenna systems which incorporates a slot-line balun.
It is a still further object of the invention to provide a reconfigurable diplexer for use in antenna systems which provides 50 dB of isolation between transmit and receive ports.
It is yet another object of the invention to provide a reconfigurable diplexer for use in dual-beam or multi-beam antenna array systems which operates substantially equivalently in at least two different, predefined frequency bands.
In accordance with the present invention there is provided a reconfigurable, tunable diplexer, which includes a slot-line balun. In one embodiment, the diplexer includes a common, slot-line transmission line adapted to carry electromagnetic signals; a pair a separate slot-line transmission lines coupled to the common transmission line; each separate slot-line transmission line having an individual filter coupled thereto, wherein each filter is adapted to selectively give its respective separate slot-line transmission line a characteristic impedance dependent upon predetermined frequencies of the electromagnetic signals; and a separate slot-line balun associated with each separate slot-line transmission line and adapted for coupling signals to and/or from its respective separate slot-line transmission line.
The inventive diplexer may be configured to operate in several different bands by configuring resonant cavities. Typically, selective operation in either the International Telecommunications Satellite Organization (INTELSAT) frequencies (13.5-14.5 GHz uplink, 11.7-12.5 GHz downlink) or Defense Satellite Communication System (DSCS) frequencies (7.8-8.4 GHz uplink, 7.2-7.6 GHz downlink) is allowed. The diplexer makes possible simultaneous transmission and reception through a single reconfigurable antenna array with relatively high isolation, typically on the order of 50 dB between the Rx and Tx channels.